Braking systems for railway vehicles include tread brakes and disc brakes. Of these, tread brakes suitably clean a wheel tread while braking by removing debris with the brake shoe itself, even if debris such as oil adheres to the wheel tread surface, and thus they do not present a problem (e.g., Patent Reference 1, Paragraph 0007).
However, disc brakes do not clean a wheel tread while braking, as tread brakes do, so there is a problem in that once debris such as oil adheres to the wheel tread surface, it causes sliding.
Therefore, if disc brakes are installed in a railway vehicle steering truck, it is necessary to install a separate system for wheel tread surface cleaning, and to clean the wheel tread surface whenever needed.
Among wheel tread surface cleaning systems which are separately installed in railway vehicle steering trucks, there are wheel tread surface cleaning systems installed on disc brake axles which include a type which uses a constant pressure spring to continuously press a cleaning element against a wheel tread, and a movable type which presses a cleaning element against a wheel tread when necessary, in response to a signal from the railway vehicle.
Of these, the former is a simple and low-cost wheel tread surface cleaning system, but since the cleaning element is continuously being pressed against the wheel tread, there is an increased wear on the cleaning element.
In particular, when such a system is installed in a steering truck, the cleaning element is formed in such a manner that it is pressed on the wheel tread, when traveling through a straight section (see FIG. 4(a)), as well as when passing through a curved section (see FIGS. 4(b) and (c)). Therefore, on an inner side of a rail where a wheel approaches a truck frame when passing through a curved section (see FIG. 4(b)), the pressing force of the cleaning element on the wheel tread is greater than in the case of an ordinary truck, so the wear increases even more.
In FIG. 4, Reference Numeral 1 is a truck frame, 2 is a wheel axle formed from a wheel 2a and an axle 2b, 3 is a cleaning element attached so as to freely oscillate via a link 4, 5 is a constant pressure spring which presses the cleaning element 3 onto a tread surface 2aa of the wheel 2a, 6 is an axle box, and 7 is an axle spring.
On the other hand, the movable type wheel tread surface cleaning system is able to reduce wear on the cleaning element, because the cleaning element presses against the wheel tread only when necessary, but there is a problem in that it has a complex mechanism, so the system itself becomes costly.